1. Field of the Invention
This invention relates generally to flatness gages and dial indicators and, more particularly, to handheld flatness gages incorporating height measuring devices such as dial indicators, particularly as used in conjunction with Almen strip holders.
2. Discussion of the Background Art
Almen strips have long been used for quality control of shot peening processes. Flat holders are used to hold the Almen strips in shot peening cells to test the effectiveness and quality of the shot peening procedure and apparatus. Almen strips are well known for use in the field of shot peening quality control, see U.S. Pat. No. 2,620,838. The Almen strips are held in Almen strip holders and shot peened in the cells. The effectiveness of the Almen strip test and its usefulness as a quality assurance procedure is very much dependant on the repeatability of the Almen strip testing procedure. There is a need to assure the flatness of a flat surface of the Almen strip holder against which the Almen strip is held during the shot peening of the Almen strip. This is not always an easy thing to do, particularly, when the Almen strip holder is mounted on a model designed to simulate the part being shot peened. Models of gas turbine engine parts such as rotor disks and blades are often built with Almen strip holders mounted at key positions to simulate the shot peening process for quality control purposes. Almen strip holder flat surfaces should be flat and in one example it should be within 0.001 inches so that the Almen intensity values are not corrupted. Holders with flat surfaces that are slightly concave or convex can reduce or increase curvature of the peened strip and produce intensity values that are too low or too high. Simple fixtures with accessible Almen strip holders can be easily checked for flatness on a surface plate but Almen strip holders that are attached or welded to scrap parts or test models are difficult, if not impossible, to check. Therefore, it is very desirable to have a handheld device that is portable and capable of checking flatness of Almen strip holders in hard to reach or otherwise inaccessible locations. It is desirable to have an easy to use flatness measuring device that allows for a quick check of the flatness of the Almen strip holder. It is also desirable that the device be portable, handheld and operated, and easily maneuverable in order to be used on model positions that are difficult to access.